The moonlets of asteroid 87 Sylvia: Remus and Romulus

1 August 2005

The observations of the moonlets’ orbits allow the astronomers to precisely calculate the mass and density of Sylvia. With a density only 20% higher than the density of water, it is likely composed of water ice and rubble from a primordial asteroid.

These asteroids are loose aggregations of rock presumably created when another asteroid smacked into it and disrupted it. A new asteroid formed later by accumulation of large fragments. The moonlets are probably debris left over from the collision that were captured by the newly formed asteroid and eventually settled into orbits around it. Because of the way they form, we expect to see more multiple asteroid systems like this. French team: